Device operable to control turning of vehicle

ABSTRACT

A device operable to control a turning of a vehicle, includes: a motion controller operable to: control a first adjuster so as to increase a drive force applied to at least one of front wheels and rear wheels situated in an inner side of the turning, and control a second adjuster so as to increase the braking force applied to at least one of the front wheels and the rear wheels situated in an outer side of the turning; and control the first adjuster so as to increase the drive force applied to at least one of the front wheels and the rear wheels situated in an outer side of the turning, and control the second adjuster so as to increase the braking force applied to at least one of the front wheels and the rear wheels situated in an inner side of the turning.

BACKGROUND

1. Field of the Invention

The present invention relates to a turning behavior control device of avehicle.

2. Description of the Related Art

Conventionally, techniques to enhance the safety of a vehicle bystabilizing the vehicle, which is turning, have been developed. Forexample, Japanese Patent Publication No. 2007-131229A described laterdiscloses a technique in which a difference of the drive force betweenthe right and the left wheel is fed back according to a yaw rate of avehicle and a braking force given to each wheel of the vehicle is alsofed back. Further, electronic control LSD (Limited Slip Differential) ofa center differential gear, in which a degree of the limitation of thedifferential between the front and the rear wheel is variable, is fedback according to the yaw rate of a vehicle.

However, in some cases, it is difficult to suppress a tendency ofover-steering, which is caused in a turning vehicle, only by executingcontrol so that a drive force of the inner turning wheel can beincreased. That is, since a load given to the outer turning wheel isincreased while the vehicle is turning and a load given to the innerturning wheel is relatively decreased, a gripping force of the innerturning wheel to grip a road surface, that is, a traction of the innerturning wheel is lowered. Therefore, even if a drive force given to theinner turning wheel is increased, the inner wheel slips and it isimpossible to generate a sufficiently high moment for suppressing thetendency of over-steering in some cases. In this connection, the abovephenomenon tends to occur in the case where the turning vehicle isaccelerated.

In the case where the turning vehicle is decelerated, not only atraction of the inner turning wheel is lowered but also a load given tothe front wheel is increased and a load given to the rear wheel isrelatively decreased and a traction of the rear wheel is lowered.Accordingly, even when a drive force control is executed between theright and the left wheel on the rear side, it is impossible to generatea sufficiently high moment to suppress the generation of under-steeringand over-steering in some cases.

In the case where under-steering is generated when a vehicle of 4-wheeldrive is turning, it is possible to adopt a method in which the tendencyof under-steering is suppressed by enhancing the turning property of avehicle by weakening the limitation of the differential between thefront and the rear wheel. However, according to this method, since atraction of the entire vehicle is decreased, the acceleratingperformance of the vehicle is lowered. That is, on the assumption thatthe rear wheel of the vehicle has slipped under the condition that adifferential between the front and the rear wheel made by the centerdifferential gear is not limited, the rear wheel is further rotated.Therefore, torque originally to be transmitted to the front wheel istransmitted to the rear wheel which is slipping. Accordingly, thevehicle is limited from being accelerated.

In order to solve the above problems, the present applicant proposed thefollowing control technique which is described in Japanese PatentPublication No. 2007-131229A. By applying the yaw rate feedback control,a limitation of the differential between the front and the rear wheel ismade by the front and rear differential limitation device and a driveforce control between the right and the left wheel of the vehicle ismade by the right and left wheel torque difference generating device andfurther the brake device is integrally controlled. Only whenover-steering is suppressed, in parallel with the control of the driveforce between the right and the left wheel of the vehicle, controllingis executed so that a restricting force generated by the differentialcontrol between the front and the rear wheel made by the centraldifferential gear is strengthened.

However, in the case where the yawing control is made by a braking forcegenerated by the braking device (four wheel independence braking device)in the manner executed by the conventional constitution, a disadvantageof the feeling of speed reduction is caused. Especially when a brakingforce is given at the time of acceleration, control is made in theopposite direction to that of the driver's will in which the driverwants to accelerate. Therefore, the feeling of speed reduction becomesremarkable. In the case where over-steering is suppressed at the time ofsudden acceleration, since the front wheel, the lateral force of whichis reduced by a drive force, is braked and the lateral force isrestored, over-steering is facilitated on the contrary. In the casewhere the vehicle is running at a low speed, deviation of the yaw rateis increased. Therefore, in the case of carrying out the suppression ofunder-steering and over-steering, the suppression is excessively made.

In the case where the yawing control is made by a right and left wheeltorque difference generating device like the conventional constitution,since a load given to the rear wheel is decreased at the time ofdeceleration, a controlling capacity is lowered. Further, thesuppression of over-steering made by a torque difference between theright and the left wheel on the rear side facilitates over-steering by areduction of the lateral force of the rear wheel on the contrary.

In the case where the yawing control is executed by the front and reardifferential limiting device, a vehicle, the behavior of which shows atendency of under-steering, is put into a state of head-in/head-outdepending upon the circumstances. Therefore, it is difficult to grasp atorque moving direction. Accordingly, it is difficult to suppressunder-steering by the differential limitation made by the front and reardifferential limiting device. Since the vehicle, the behavior of whichshows a tendency of over-steering, is always put into a state ofhead-out, by the differential limitation made by the front and reardifferential limiting device, the front wheel is given a drive force andthe rear wheel is given a braking force. Therefore, when thedifferential limitation for suppressing over-steering is executed at thetime of deceleration, the rear wheel, which is being braked, is furtherbraked, which is a factor of facilitating over-steering.

SUMMARY

According to one aspect of the invention, there is provided a deviceoperable to control a turning of a vehicle, including: a first adjuster,operable to adjust a drive force applied to at least one of front wheelsand rear wheels of the vehicle; a second adjuster, operable to adjust abraking force applied to at least one of the front wheels and the rearwheels; a first detector, operable to detect an acceleration anddeceleration of the vehicle and a motion controller, operable to providea control amount which is distributed to the first adjuster with a firstratio and to the second adjuster with a second ratio, the motioncontroller operable to: control the first adjuster so as to increase thedrive force applied to the at least one of the front wheels and the rearwheels situated in an inner side of the turning, and control the secondadjuster so as to increase the braking force applied to at least one ofthe front wheels and the rear wheels situated in an outer side of theturning, in order to suppress yawing of the vehicle; control the firstadjuster so as to increase the drive force applied to at least one ofthe front wheels and the rear wheels situated in an outer side of theturning, and control the second adjuster so as to increase the brakingforce applied to at least one of the front wheels and the rear wheelssituated in an inner side of the turning, in order to facilitate theyawing; increase the first ratio in a case that the first detectordetects the acceleration; and increase the second ratio in a case thatthe first detector detects the deceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment may be described in detail with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic block diagram showing an overall arrangement of aturning behavior control device of a vehicle of a first embodiment ofthe present invention;

FIG. 2 is a schematic control block diagram mainly showing control madeby a turning behavior control device of a vehicle of the firstembodiment of the present invention;

FIG. 3 is a table showing a characteristic of strength and weakness ofan amount of control of a turning behavior control device of a vehicleof the first embodiment;

FIGS. 4A to 4E are views showing an example of a control characteristicmap of a turning behavior control device of a vehicle of the firstembodiment;

FIG. 5 is a flow chart showing control of a turning behavior controldevice of a vehicle of the first embodiment;

FIG. 6 is a flow chart showing control of a turning behavior controldevice of a vehicle of the first embodiment and also showing asub-routine of OS suppression control;

FIG. 7 is a flow chart showing control of a turning behavior controldevice of a vehicle of the first embodiment of the present invention andthis flow chart shows a sub-routine of US suppression control;

FIG. 8 is a schematic block diagram showing an overall arrangement of aturning behavior control device having a central differential gear of asecond embodiment of the present invention;

FIG. 9 is a schematic control block diagram mainly showing control of aturning behavior control device of a vehicle of the second embodiment;

FIG. 10 is a table showing a characteristic of strength and weakness ofan amount of control of a turning behavior control device of a vehicleof the second embodiment;

FIGS. 11A to 11E are views showing an example of a controlcharacteristic map of a turning behavior control device of a vehicle ofthe second embodiment;

FIG. 12 is a flow chart showing control of a turning behavior controldevice of a vehicle of the second embodiment;

FIG. 13 is a flow chart showing control of a turning behavior controldevice of a vehicle of the second embodiment and this flow chart shows asub-routine of OS suppression control; and

FIG. 14 is a flow chart showing control of a turning behavior controldevice of a vehicle of the first embodiment of the present inventionwhere this flow chart shows a sub-routine of US suppression control.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, a first embodiment of the present inventionwill be explained below. The turning behavior control device shown inFIG. 1 is applied to a four-wheel drive type vehicle 1. An output of theengine 2 mounted on the vehicle 1 is transmitted to the right frontwheel 8R and the left front wheel 8L through the transmission 3, theintermediate gear mechanism 4, the front differential gear 6 and theaxles 7R, 7L. At the same timer the output of the engine 2 mounted onthe vehicle 1 is transmitted to the right rear wheel 14R and the leftrear wheel 14L through the hypoid gear mechanism 9 on the front wheelside, the propeller shaft 10, the hypoid gear mechanism 11 on the rearwheel side, the rear differential gear 12 and the axles 13R, 13L. To bein more detail, this rear differential gear 12 includes a drive forcemoving mechanism 15 for moving a drive force between the right and theleft wheel, the detail of which will be described later.

The front differential gear 6 is a torque induction type differentialgear which mechanically restricts a differential motion made between theright 8R and the left wheel 8L according to an intensity of torqueinputted from the engine 2.

Next, a drive system on the rear wheel 14 side will be explained below.In this rear wheel 14, the rear differential gear 12 is provided whichallows a differential motion made between the right wheel 14R and theleft wheel 14L. In this rear differential gear 12, the drive forcemoving mechanism 15 for moving a drive force between the right and theleft wheel is provided, by which a difference of the drive force to betransmitted to the right wheel 14R and the left wheel 14R can beappropriately changed.

On the outer circumference of the case 12A of this rear differentialgear 12, the crown gear 16, which is meshed with the pinion gear 10Aprovided at a rear end portion of the propeller shaft 10, is arranged.Inside the case 12A, the planetary gear mechanism 12B is provided. Bythis planetary gear mechanism 12B, a differential motion between theright wheel 14R and the left wheel 14L is allowed. Accordingly, torque,which has been inputted from the engine 2 into the crown gear 16 throughthe propeller shaft 10 and the pinion gear 10A, is transmitted to bothwheels 14R, 14L while a differential motion between the right rear wheel14R and the left rear wheel 14L is being allowed by the planetary gearmechanism 12B.

The drive force moving mechanism 15 for moving a drive force between theright and the left wheel includes: a change gear mechanism ISA; and atorque transmission mechanism 15B of a variable transmission capacitycontrol type. By a command given from ECU 40 mounted on the vehicle 1, adifference between the drive force of the right wheel 14R and that ofthe left wheel 14L can be appropriately changed according to a runningstate of the vehicle. In this structure, the change gear mechanism 15Aincreases and decreases a rotary speed of one of the right and the leftwheel (in this case, a rotary speed of the left wheel 14L) and outputsit to the torque transmission mechanism 15B.

This variable transmission capacity control type torque transmissionmechanism 15B is a wet hydraulic type multiple disk clutch mechanismcapable of adjusting a transmission torque capacity according tohydraulic pressure inputted from a drive system hydraulic unitcontrolled by ECU 40. This variable transmission capacity control typetorque transmission mechanism 15B is operated as follows. By utilizing adifference between the rotary speed, which is increased or decreased bythe change gear 15A, and the rotary speed of the other wheel (in thepresent embodiment, the right wheel 14R) in the right and the leftwheel, torque is given and received between the right wheel 14R and theleft wheel 14L. Due o the foregoing, an intensity of torque of one wheelis increased or decreased and an intensity of torque of the other wheelis decreased or increased. In this connection, the planetary gearmechanism 12B, the change gear mechanism 15A and the torque transmissionmechanism 15B described above are well known. Therefore, the detailedexplanations of the structures of the above mechanisms are omitted here.Hydraulic pressure inputted from the drive system hydraulic unit intothe drive force moving mechanism 15 for moving a drive force between theright and the left wheel is controlled by the rear differential gearcontroller 31. Contents of this control will be described in detaillater.

Accordingly, for example, in the case where the vehicle 1 is going aheadwhile it is turning clockwise, a predetermined hydraulic pressure isinputted from a drive system hydraulic unit (not shown) into the driveforce moving mechanism 15 for moving a drive force between the right andthe left wheel of the rear differential gear 12. When the predeterminedhydraulic pressure is transmitted to the right wheel 14R and the torqueis decreased, the right rear wheel 14R is decelerated. At this time,torque transmitted to the left rear wheel 14L is increased and the leftrear wheel 14L is accelerated. Accordingly, it is possible to generate ayaw moment, the direction of which is clockwise, in the vehicle 1.

In this connection, the above drive system hydraulic unit not shown inthe drawing includes: an accumulator; a motor pump for pressurizinghydraulic oil in the accumulator at a predetermined pressure; a pressuresensor for monitoring hydraulic pressure pressurized by the motor pump;an electromagnetic control valve for adjusting hydraulic pressure in theaccumulator which has already been adjusted by the motor pump; and adirection change-over valve for changing over the hydraulic pressure,which has been adjusted by the electromagnetic control valve, between apredetermined hydraulic chamber (not shown) of the drive force movingmechanism 15 for moving a drive force between the right and the leftwheel and a predetermined hydraulic chamber (not shown) of thedifferential motion restricting mechanism for restricting a differentialmotion between the front 19 and the rear wheel.

The rear differential gear controller 31 (a first adjuster) is anelectronic control unit having an interface, memory and CPU which arenot shown in the drawing. This rear differential gear controller 31 isoperated as follows. A signal (a drive force distribution signal)showing a hydraulic pressure corresponding to a drive force differencebetween the right rear wheel 14R and the left rear wheel 14L and alsoshowing an output destination of the hydraulic pressure is sent to thedrive system hydraulic unit. When the drive system hydraulic unit, whichhas received this drive force difference signal, appropriately controlshydraulic pressure for the drive force moving mechanism 15 for moving adrive force between the right and the left wheel of the reardifferential gear 12, a difference of the drive force between the rightrear wheel 14R and the left rear wheel 14L is adjusted.

Wheels 8L, 8R, 14L, 14R of the vehicle 1 respectively have brakingdevices 21L, 21R, 22L, 22R. Control system hydraulic units forindependently supplying hydraulic pressure to the braking devices 21L,21R, 22L, 22R are provided. This vehicle 1 has a brake device controller(a second adjuster) 33, This brake device controller 33 is an electroniccontrol unit having an interface, memory and CPU which are not shown inthe drawing. This brake device controller 33 sends a signal (a brakeincreasing and decreasing pressure signal), which shows hydraulicpressure to be increased and decreased with respect to the fourrespective brake devices 21L, 21R, 22L, 22R arranged in the wheels 8L,8R, 14L, 14R, to a control system hydraulic unit (not shown) . Thecontrol system hydraulic unit, which has received this brake increaseand decrease pressure signal, appropriately controls hydraulic pressureinputted into the brake device 21L, 21R, 22L, 22R. This braking systemhydraulic unit includes a motor pump and an electromagnetic controlvalve for adjusting braking hydraulic pressure, so that a predeterminedhydraulic pressure can be inputted into each braking unit 21L, 21R, 22L,22R according to a direction given from the braking unit controller 33.As described above, the rear differential controller 31 and the brakingunit controller 33 are connected to ECU 40 through signal lines andoperated according to a control signal sent from ECU 40.

ECU 40 is an electronic control unit having an interface, memory and CPUwhich are not shown in the drawing. ECU 40 can read in the result of thedetection made by the vehicle speed sensor (a second detector) 45L, 45R,46L, 46R, the steering angle sensor 47, G sensor (a first detector) 48and the yaw rate sensor 49.

This ECU 40 includes a control yaw moment calculation portion 41, anunder-steering/over-steering judging portion (US/OS judging) 42 and ayawing motion control portion (a motion controller) 43 which areprograms recorded in a memory not shown. The yawing motion control map44 used by the yawing motion control portion 43 is recorded in thismemory. The control yaw moment calculation portion 41 is provided forfinding a control yaw moment which is a yaw moment to be added so thatthe vehicle 1 can be turned by a turning radius at which the driverintends to turn the vehicle.

As shown in FIG. 2, this control yaw moment calculation portion 41calculates a target yaw rate (target yaw momentum correlation value)according to a steering angle, which is measured by the steering anglesensor 47, and a vehicle speed which is detected by each wheel speedsensor. Further, when this control yaw moment calculation portion 41executes control in which a correction is made by comparing the targetyaw rate with the actual yaw rate measured by the yaw rate sensor 49,that is, when this control yaw moment calculation portion 41 executesfeedback control according to the actual yaw rate, the control yawmoment can be calculated.

US/OS judging portion 42 is provided for judging a turning state of thevehicle 1 that is turning. According to the control yaw moment obtainedby the control yaw moment calculation portion 41 and also according tothe acceleration in the lateral direction of the vehicle 1 measured by Gsensor 49, it is judged whether the turning vehicle 1 is in a state(under-steering state) in which under-steering (US) is being generated,the turning vehicle 1 is in a state (neutral-steering state) in whichneither under-steering (US) nor over-steering (OS) is actually beinggenerated or the turning vehicle 1 is in a state (over-steering state)in which over-steering is being generated.

When the yawing motion control portion 43 controls the rear differentialcontroller 31 and the braking unit controller 33 according to a turningstate of the vehicle 1, a yaw moment corresponding to the control yawmoment is generated in the vehicle 1. That is, when the control yawmoment obtained by the control yaw moment calculation portion 41, theresult of the judgment (the turning state of the vehicle 1) made byUS/OS judging portion 42 and the acceleration (longitudinalacceleration) in the longitudinal direction of the vehicle 1 detected(measured) by G sensor 49 are applied to the yawing motion control map44, control values for controlling the rear differential gear controller31 and the braking unit controller 33 are obtained.

In this case, the control value for the rear differential controller 31is a value showing a degree of the drive force movement between theright wheel 14R and the left wheel 14L made by the drive force movingmechanism 15 for moving a drive force between the right and the leftwheel of the rear differential gear 12. Specifically, the control valuefor the rear differential controller 31 is a hydraulic value of thedrive force moving mechanism 15 for moving a drive force between theright and the left wheel. The control value for the braking unitcontroller 33 is a value showing a degree of an increase and decrease ofthe braking force of each braking unit 21L, 21R, 22L, 22R. Specifically,the control value for the braking unit controller 33 is a value ofincreasing or decreasing a hydraulic pressure of each braking unit 21L,21R, 22L, 22R.

Next, the yawing motion control map 44 will be explained below. As shownin FIGS. 4A to 4E, the yawing motion control map 44 of the presentembodiment is composed of a plurality of maps. FIG. 4A is a basic map.FIG. 4B is a map selected at the time of accelerating the vehicle. FIG.4C is a map selected at the time of decelerating the vehicle. FIG. 4D isa map selected at the time of high speed running of the vehicle. FIG. 4Eis a map selected at the time of low speed running of the vehicle. Abasic arrangement of the map is explained below referring to FIG. 4 Awhich represents the above maps. The axis of abscissas prescribes adegree of under-steering (US) generated in the vehicle 1 which is foundfrom a turning state of the vehicle 1, that is, which is found from thecontrol yaw moment obtained by the control yaw moment calculationportion 41 and from the result of the judgment made by US/OS judgingportion 42. Alternatively, the axis of abscissas prescribes a degree ofover-steering (OS). On the other hand, the axis of ordinate prescribesan absolute value of the control value for the rear differential gearcontroller 31 and the braking device controller 33. Besides, the highspeed means a speed that is no less than a prescribed value, and the lowspeed means a speed that is less than the prescribed value.

As shown in FIG. 2, the yawing motion control map 44 mainly prescribesan over-steering suppression region 44A and an under-steeringsuppression region 44B. In this over-steering suppression region 44A,the rear differential control region 44A1 and the braking control region44A2 are prescribed in the order of the control yaw moment, wherein thelowest control yaw moment is arranged first. In the under-steeringsuppression region 44B, the rear differential control region 44B1 andthe braking control region 44B2 are prescribed in the order of thecontrol yaw moment in which the lowest control yaw moment is arrangedfirst.

In the case where the yawing motion of the vehicle 1 is suppressed, thatis, in the case where over-steering (OS) generated in the vehicle 1 issuppressed, the yawing motion control portion 43 controls the reardifferential gear controller 31 so that a drive force of the wheel(inner turning wheel), which is a wheel in the right wheel 14R and theleft wheel 14L located on the turning center side, can be increased. Inthe case where over-steering (OS) generated in the vehicle 1 issuppressed and only in the case where a control yaw moment can not bestill generated even when the rear differential controller 31 carriesout a drive control between the right and the left wheel, the yawingmotion control portion 43 controls the braking device controller 33 sothat the braking force of the outer turning wheel can be stronger thanthe braking force of the inner turning wheel.

On the other hand, in the case where the yawing motion of the vehicle 1is facilitated, that is, in the case where under-steering (US) generatedin the vehicle 1 is suppressed, the yawing motion control portion 43controls the rear differential gear controller 31 so that a drive forceof the wheel (turning outer wheel) on the opposite side to the innerturning wheel in the right wheel 14R and the left wheel 14L can beincreased. In the case where under-steering (US) generated in thevehicle 1 is suppressed and only in the case where a control yaw momentcan not be still generated even when the rear differential controller 31carries out a drive control between the right and the left wheel, theyawing motion control portion 43 controls the braking device controller33 so that the braking force of the inner turning wheel can be strongerthan the braking force of the outer turning wheel.

That is, in the case of suppressing the yawing motion of the vehicle (atthe time of the generation of OS), the yawing motion control portion 43distributes an amount of control to the rear differential gearcontroller 31 and the braking device controller 33 and while the reardifferential gear controller 31 is being controlled so that a driveforce of the inner turning wheel can he increased, the braking devicecontroller 33 is controlled so that a braking force of the outer turningwheel can be increased. In the case of facilitating the yawing motion ofthe vehicle (at the time of the generation of US), the yawing motioncontrol portion 43 distributes an amount of control to the reardifferential gear controller 31 and the braking device controller 33 andwhile the rear differential gear controller 31 is being controlled sothat a drive force of the outer turning wheel can be increased, thebraking device controller 33 is controlled so that a braking force ofthe inner turning wheel can be increased. At the same time, in the caseof facilitating the yawing motion of the vehicle (at the time of thegeneration of US), a ratio of the amount of control to be distributed tothe rear differential controller 31 is made to be higher than the ratioof the amount of control to be distributed in the case where the yawingmotion of the vehicle is suppressed (at the time of the generation ofOS). In the case of suppressing the yawing motion of the vehicle (at thetime of the generation of OS) , a ratio of the amount of control to bedistributed to the braking device controller 33 is made to be higherthan the ratio of the amount of control to be distributed in the casewhere the yawing motion of the vehicle is facilitated (at the time ofthe generation of US). The yawing motion control map 44 having the abovecontrol characteristic is provided.

The basic control characteristic in the case of using the yawing motioncontrol map 44 is described above. The yawing motion map 44 is set indetail not only for the case of under-steering (US) and over-steering(OS) but also for the case in which an absolute value of controlling iscontrolled being changed according to the acceleration, deceleration andspeed of the vehicle and an amount of the distribution of the controlbetween the drive force moving mechanism 15 for moving a drive forcebetween the right and the left wheel and the braking unit is controlledbeing changed as shown in FIGS. 4A to 4E. That is, a distribution of theamount of control between the rear differential controller 31 and thebraking unit controller 33 can be changed according to the acceleration,deceleration and speed of the vehicle. The characteristic of thedistribution of the amount of control is previously set according to theyawing motion control map 44 shown in FIGS. 4A to 4E.

In the case where the result of the detection made by G sensor 49 is anacceleration (shown in FIG. 4B), the yawing motion control map 44 makesa ratio of the amount of control distributed to the rear differentialcontroller 31 to be higher than a ratio in the case of deceleration(shown in FIG. 4C). In the case where the result of the detection madeby G sensor 49 is a deceleration (shown in FIG. 4C), the yawing motioncontrol map 44 makes a ratio of the amount of control distributed to thebraking unit controller 33 to be higher than a ratio in the case ofacceleration (shown in FIG. 4B). In the case where the result of thedetection made by the wheel speed sensor is a low speed (shown in FIG.4E), a ratio of the amount of control distributed to the reardifferential controller 31 is made to be higher than the ratio in thecase of a high speed (shown in FIG. 4D) . In the case where the resultof the detection made by the wheel speed sensor is a high speed (shownin FIG. 4E), a ratio of the amount of control distributed to the brakingunit controller 33 is made to be higher than the ratio in the case of alow speed (shown in FIG. 4F). The characteristic is set as describedabove. The characteristic of the intensity of the amount of control isshown in FIG. 3. The rear differential gear shows a rear differentialcontroller 31 (drive force moving mechanism 15 for moving a drive forcebetween the right and the left wheel). The brake shows a braking unitcontroller 33 (braking device 21L, 21R, 22L, 22R). Further, “High”,“Middle” and “Low” are heights of the absolute values of the devices,that is, “High”, “Middle” and “Low” are values of the hydraulic pressureof the devices. These values are previously stored in ECU 40.

The turning behavior control device of a vehicle of the embodiment ofthe present invention is composed as described above. Therefore, itexhibits the following action and effect. Contents of the action andeffect will be explained referring to the flow charts shown in FIGS. 5to 7.

As shown in FIG. 5, in step S11, the control yaw moment calculatingportion 41 reads in a steering angle detected by the steering sensor 47,a vehicle speed detected by each vehicle speed sensor 45 and an actualyaw rate detected by the yaw rate sensor 48. At the same time, US/OSjudging portion 42 reads in a lateral acceleration detected by G sensor49.

In step S12, the control yaw moment calculating portion 41 calculates atarget yaw rate according to the steering angle and the vehicle speedthat was read in before. When the target yaw rate and the actual yawrate are compared with each other, the control yaw moment calculatingportion 41 calculates a control yaw moment. After that, in step S13, amap (shown in FIGS. 4A to 4E) corresponding to the speed and theacceleration and deceleration is selected.

In steps S14 and S16, according to the control yaw moment and thelateral acceleration, US/OS judging portion 42 judges whetherover-steering (OS) is generated in the vehicle 1, under-steering (US) isgenerated in the vehicle 1 or neither under-steering (US) norover-steering (OS) is substantially generated. In the case where US/OSjudging portion 42 judges that the vehicle 1 is in a state in whichover-steering has been generated, the program proceeds to step S15 andOS suppression control, which is a sub-routine, is carried out. WhenUS/OS judging portion 42 judges in step 16 that under-steering isgenerated, the program proceeds to step S17 and US suppression control,which is a sub-routine, is carried out. In the case where US/OS judgingportion 42 judges that neither under-steering nor over-steering isgenerated, the program returns as it is.

Next, OS suppression control and US suppression control, which aresub-routines, will be explained below. In OS suppression control shownin FIG. 6, when torque moving control (rear differential gear control)made between the right rear wheel 14R and the left rear wheel 14L by therear differential gear controller 31 is carried out by the reardifferential gear controller 31 in step S21, it is judged whether or notthe control yaw moment can be satisfied.

In this case, when it is judged that the control yaw moment can besatisfied by carrying out the rear differential gear control, in stepS22, the rear differential control is carried out according to thecharacteristic of the selected map. Due to the foregoing, a differencein torque between the right rear wheel 14R and the left rear wheel 14Lis adjusted, so that over-steering generated in the vehicle 1 can besuppressed.

On the other hand, in the case where it is judged that the control yawmoment can not be satisfied even if the rear differential gear controlis executed, in step S23, in addition to the rear differential gearcontrol corresponding to the characteristic of the selected map, thecontrol (the brake control) executed by the braking device controller33, in which the braking force given to the outer turning wheel is madeto be stronger than the braking force given to the inner turning wheel,is carried out. Due to the foregoing, over-steering generated in thewheel 1 is suppressed.

US suppressing control shown in FIG. 7 will be explained as follows. Instep S31, when the rear differential gear control is carried out, it isjudged whether or not the control yaw moment can be satisfied. In thiscase, when it has been judged that the control yaw moment can besatisfied by carrying out the rear differential gear control, in stepS32, the rear differential gear control is carried out corresponding tothe characteristic of the selected map, so that a difference of torquebetween the right rear wheel 14R and the left rear wheel 14L can beadjusted. In this way, under-steering generated in the vehicle 1 issuppressed.

In the case where it has been judged that the control moment can not besatisfied only when the rear differential gear control is carried out,in step S33, in addition to the rear differential gear control, thebraking control is carried out corresponding to the characteristic ofthe selected map, so that under-steering generated in the vehicle 1 canbe suppressed.

As described above, in the present embodiment, in the case ofsuppressing the yawing motion of the vehicle 1, a drive force of theinner turning wheel is increased and a braking force of the outerturning wheel is increased. In the case of facilitating the yawingmotion of the vehicle, a drive force of the outer turning wheel isincreased and a braking force of the inner turning wheel is increased.Accordingly, the turning performance of the vehicle can be enhanced. Atthe time of suppressing the yawing motion and at the time offacilitating the yawing motion, an amount of the distribution of thecontrol between the rear differential gear controller 31 and the brakingdevice controller 33 is controlled being changed. Therefore, as comparedwith a case in which the amount of the distribution of the control isfixed, it is possible for the case of the present embodiment canflexibly cope with a state of the vehicle. Accordingly, a drive feelingcan be enhanced.

That is, in the case of facilitating the yawing motion of the vehicle(at the time of the generation of US), a ratio of the amount of thecontrol distributed to the rear differential gear controller 31 is madeto be higher than the ratio in the case of suppressing the yawing motionof the vehicle (at the time of the generation of OS). Therefore, a driveforce of the outer turning wheel, the ground contact load of which isheavy, is increased so that the yawing motion control can be effectivelyexecuted. In the case of suppressing the yawing motion of the vehicle 1(at the time of the generation of OS), a ratio of the amount of thecontrol distributed to the braking unit controller 33 is made to behigher than the ratio in the case of facilitating the yawing motion ofthe vehicle 1 (at the time of the generation of US). Therefore, a driveforce of the outer turning wheel, the ground contact load of which isheavy, is increased so that the yawing motion control can be effectivelyexecuted and the turning performance can be stabilized.

In the present embodiment, in the case where the map shown in FIG. 4B isselected in step S13 of FIG. 5, a ratio of the amount of the controldistributed to the rear differential controller 31 is made to he higherthan the ratio of the case of deceleration shown in FIG. 4C. Therefore,at the time of acceleration in which a ground contact load of the wheelis increased, the drive force is more increased so that the yawingmotion control can be more effectively executed. Accordingly, while afeeling of deceleration at the time of acceleration is being decreased,the turning performance can be stabilized and the drive feeling can bemore enhanced. At the time of deceleration of the vehicle 1 and in thecase where the map shown in FIG. 4C is selected in step S13 shown inFIG. 5, a ratio of the amount of the control distributed to thecontroller 33 of the braking unit is made to be higher than the ratio inthe case of acceleration shown in FIG. 4C. Therefore, even when thewheel load is reduced due to deceleration, a decrease in the lateralforce of the wheel caused by an increase in the difference of the driveforce between the right wheel and the left wheel can be suppressed.Accordingly, the turning performance at the time of deceleration can bestabilized.

In the present embodiment, when the vehicle is running at a low speedand the map shown in FIG. 4E is selected in step S13 shown in FIG. 5, aratio of the amount of the control distributed to the rear differentialcontroller 31 is made to be higher than the ratio of the case of a highspeed shown in FIG. 4D. When the vehicle is running at a high speed andthe map shown in FIG. 4D is selected in step S13 shown in FIG. 5, aratio of the amount of the control distributed to the controller 33 ofthe braking unit is made to he higher than the ratio of the case of alow speed shown in FIG. 4E. Therefore, while a feeling of decelerationcaused by in increase in an excessively strong braking force is beingsuppressed, under-steering and over-steering can be properly suppressedand the turning performance of the vehicle can be enhanced.

Next, referring to FIGS. 8 to 14, a second embodiment of the presentinvention will be explained as follows. With respect to the arrangementof the first embodiment, the vehicle 1A of the present embodiment shownin FIG. 8 includes: a central differential gear 5; a differentiallimiting mechanism 19 for limiting a differential between a front and arear wheel; and a central differential gear controller 32 (a thirdadjuster) for adjusting a degree of the limitation of the differentialbetween the front and the rear wheel by controlling the differentiallimiting mechanism 19 for limiting a differential motion between a frontand a rear wheel. The above points are different from the points of thefirst embodiment in the constitution of hardware. Further, contents ofthe control made by ECU 40A, which is a controller mounted on thevehicle 1A, are different. Therefore, like reference marks are used toindicate like components in the first and the second embodiment and thedetailed explanations are omitted here. Only different constitution andcontrol are mainly explained here.

An output of the engine 2 mounted on the four-wheel-drive type vehicle 1is transmitted to the central differential gear 5 through thetransmission 3 and the intermediate gear mechanism 4.

To be in more detail, the central differential gear 5 is provided withthe differential limiting mechanism 19 for limiting a differentialmotion between a front and a rear wheel. An output of this centraldifferential gear 5 is transmitted to the right wheel 8R and the leftwheel 8L through the front differential gear 6 and the axles 7R, 7L. Atthe same time, the output of this central differential gear 5 istransmitted to the right wheel 14R and the left wheel 14L of the rearwheels 14 through the front wheel side hypoid gear mechanism 9, thepropeller shaft 10, the rear side hypoid gear mechanism 11, the reardifferential gear 12 and the axles 13R, 13L.

The center differential gear 5 includes: differential pinions 5A, 5B;and side gears 5C, 5D meshed with the differential pinions 5A, 5B.Torque inputted from the differential pinions 5A, 5B is transmitted tothe front wheel 8 through one side gear 5C and at the same timetransmitted to the rear wheel 14 through the other side gear 5D, thepropeller shaft 10 and others. Since a differential motion between thefront wheel 8 and the rear wheel 14 is allowed by the centerdifferential gear 5 at this time, the turning property of the vehicle 1is not obstructed.

This center differential gear 5 includes a mechanism 19 for limiting adifferential motion between the front and the rear wheel capable ofvariably distributing toque, which has been outputted from the engine 2,to the front wheel 8 and the rear wheel 14 while a differential motionallowed between the front wheel 8 and the rear wheel 14 is beingvariably limited.

The mechanism 19 for limiting a differential motion between the frontand the rear wheel includes a wet type hydraulic multiple disk clutchmechanism. Therefore, according to the hydraulic pressure inputted froma drive system hydraulic unit (not shown), the mechanism 19 for limitinga differential motion between the front and the rear wheel can adjust adegree of the limitation of the differential motion between the frontwheel 8 and the rear wheel 14. Accordingly, a distribution of torque(drive force) transmitted to the front wheel 8 and the rear wheel 14 canbe appropriately changed by this mechanism. In this connection,hydraulic pressure, which has been inputted from the drive systemhydraulic unit into the mechanism 19 for limiting a differential motionbetween the front and the rear wheel, is controller by the centerdifferential controller 32. This point will be described later.

Therefore, according to the mechanism 19 for limiting a differentialmotion between the front and the rear wheel, when a degree of thelimitation of a differential motion is adjusted, the tractionperformance of the vehicle 1 can be enhanced. On the other hand, when adifferential motion between the front wheel 8 and the rear wheel 14 isallowed, the turning property of the vehicle 1 can be enhanced.

The center differential controller 32 (the third adjuster) is anelectronic control unit including an interface, memory and CPU not shownin the drawing. This center differential controller 32 is operated asfollows. A signal indicating hydraulic pressure corresponding to adegree of the limitation of a differential motion between the frontwheel 8 and the rear wheel 14 and a signal indicating the outputdestination of the hydraulic pressure (a signal of the limitation of adifferential motion between the front and the rear wheel) are sent tothe drive system hydraulic unit. When the drive system hydraulic unit,which has received this signal of the limitation of a differentialmotion between the front and the rear wheel, properly controls hydraulicpressure for the mechanism 19 for limiting a differential motion betweenthe front and the rear wheel of the central differential gear 5, adegree of the limitation of a differential motion between the frontwheel 8 and the rear wheel 14 is adjusted.

ECU 40A is an electronic control unit including an interface, memory andCPU not shown in the drawing. This ECU 40A can read in the result of themeasurement made by the wheel speed sensor (the second detector) 45L,45R, 46L, 46R, the steering angle sensor 47, G sensor (the firstdetector) 48 and the yaw rate sensor 49.

This ECU 40A has a program recorded in a memory not shown in the drawingand this program includes a control yaw moment calculating portion 41,an under-steering/over-steering judging portion (US/OS judging portion)42 and a yawing motion control portion (the motion controller) 43A. Inthis memory, the yawing motion control map 440 used by the yawing motioncontrol portion 43A is recorded. In this connection, functions of thecontrol yaw moment calculating portion 41 and US/OS judging portion 42are the same as those of the first embodiment. Therefore, theexplanations are omitted here.

The yawing motion control portion 43A controls a rear differentialcontroller 31, a central differential controller 32 and a braking unitcontroller 33 according to a turning state of the vehicle 1, so that ayaw moment corresponding to the control yaw moment can be generated inthe vehicle 1A.

According to the control yaw moment obtained by the control yaw momentcalculating portion 41, the result of the judgment made by US/OS judgingportion 42 (the turning state of the vehicle 1) and the acceleration(the acceleration in the longitudinal direction) of the vehicle 1measured by G sensor 49, these values are applied to the yawing motioncontrol map 440. In this way, the yawing motion control portion 43Aobtains control values with respect to the rear differential controller31, the central differential controller 32 and the braking unitcontroller 33.

The control value for the rear differential controller 31 is a hydraulicvalue of the mechanism 15 for moving a drive force between the right andthe left wheel. The control value for the brake unit controller 33 is ahydraulic pressure increase and decrease value of each braking unit 21L,21R, 22L, 22R. The control value for the central differential controller32 is a value expressing a degree of the differential regulation betweenthe front and the rear wheel executed by the differential limitingmechanism 19 for limiting a differential between the front and the rearwheel of the central differential gear 5. More particularly, the controlvalue for the central differential controller 32 is a hydraulic value ofthe differential limiting mechanism 19 for limiting a differentialbetween the front and the rear wheel.

Next, the yawing moment control map 440 will be explained below. In thepresent embodiment, as shown in FIGS. 11A to 11E, the yawing momentcontrol map 440 is formed out of a plurality of maps. The map shown inFIG. 11A is a basic one. FIG. 11B is a map selected at the time ofacceleration of the vehicle. FIG. 11C is a map selected at the time ofdeceleration of the vehicle. FIG. 11D is a map selected at the time ofrunning of the vehicle at a high speed. FIG. 11E is a map selected atthe time of running of the vehicle at a low speed. By using the mapshown in FIG. 11A which represents all maps, a basic structure of themap will be explained as follows. The axis of abscissas of the yawingmotion control map 440 prescribes a turning state of the vehicle 1, thatis, a degree of under-steering (US) or a degree of over-steering (OS)generated in the vehicle 1, which is found from the control yaw momentobtained by the control yaw moment calculating portion 41 and found fromthe result of the judgment made by US/OS judging portion 42, isprescribed. On the other hand, the axis of ordinate prescribes absolutevalues of the controls values for the rear differential gear controller31, the central differential gear controller 32 and the braking unitcontroller 33.

As shown in FIG. 9, the over-steering suppression region 440A and theunder-steering suppression region 440B are mainly prescribed in theyawing motion control map 440. In this over-steering suppression region440A, the rear differential gear control region 440A1, the centraldifferential gear control region 440A2 and the braking control region440A3 are prescribed in the order of the control yaw moment, wherein thelowest control yaw moment is arranged first. The rear differential gearcontrol region 440B1 and the brake control region 440B2 are prescribedin the under-steering suppression region 440B in the order of thecontrol yaw moment in which the lowest control yaw moment is arranged atthe first.

In the case of suppressing the yawing motion of the vehicle 1, that is,in the case of suppressing over-steering generated in the vehicle 1, theyawing motion control portion 43A is operated as follows. First, therear differential controller 31 is controlled so that a drive force ofthe wheel in the right wheel 14R and the left wheel 14L, which islocated on the turning center side, that is, a drive force of the innerturning wheel can be increased. Next, the center differential gearcontroller 32 is controlled so that a restriction of the differentialmotion between the front wheel 8 and the rear wheel 14 can bestrengthened. In the case where over-steering generated in the vehicle1A is suppressed and only in the case where the control yaw moment cannot be generated even when the control of a drive force between theright and the left wheel is carried out by the rear differential gearcontroller 31 and even when the control of the limitation of thedifferential motion between the front and the rear wheel is carried outby the central differential gear controller 32, the yawing motioncontrol portion 43A controls the braking unit controller 33 so that abraking force of the outer turning wheel can become stronger than abraking force of the inner turning wheel.

That is, the yawing motion control portion 43A is provided with theyawing motion control map 440 for controlling the yawing motion of thevehicle 1A by controlling at least one the yawing motion adjuster out ofthe rear differential gear controller 31, the central differential gearcontroller 32 and the braking unit controller 33. The yawing motioncontrol portion 43A is capable of changing a distribution of the amountof control of the rear differential gear controller 31, the centraldifferential gear controller 32 and the braking unit controller 33. Thecharacteristic of the distribution of the amount of control ispreviously set by the yawing motion control map 440 shown in FIGS. 11Ato 11E.

In the case were the result of the detection made by G sensor 49 is adeceleration (shown in FIG. 11C), the yaw motion control portion 43A ofthe present embodiment makes an amount of the distribution of control,which is executed by the center differential controller 32, to besmaller than an amount of the distribution of control executed by thecentral differential gear controller 32 in the case of accelerationshown in FIG. 11B. In the case where the yawing motion of the vehicle 1Ais suppressed (at the time of the generation of OS) and in the casewhere a target yawing momentum correlative value can not be satisfiedeven when the rear differential controller 31 and the centraldifferential controller 32 are controlled, the yaw motion controlportion 43A of the present embodiment controls the braking unitcontroller 33 so that a braking force of the outer turning wheel can beincreased. This point is different from the yawing potion controlportion 43 of the first embodiment.

Absolute values of control corresponding to the acceleration,deceleration and speed of the vehicle and amounts of the controldistribution between the mechanism 15 of moving a drive force betweenthe right and the left wheel and the braking unit are the same as thoseof the first embodiment.

In the case where the result of the detection made by G sensor 49 is anacceleration (shown in FIG. 11B), the yawing motion control map 440makes a ratio of the amount of control distributed to the reardifferential controller 31 to be higher than that of the case of adeceleration (shown in FIG. 11C). In the case where the result of thedetection made by G sensor 49 is a deceleration (shown in FIG. 11C), theyawing motion control map 440 makes a ratio of the amount of controldistributed to the braking unit controller 33 to be higher than that ofthe case of an acceleration (shown in FIG. 11B) In the case where theresult of the detection of each wheel speed sensor is a low speed (shownin FIG. 11 E), a ratio of the amount of control distributed to the reardifferential controller 31 is made to be higher than that of the case ofa high speed (shown in FIG. 11D). In the case where the result of thedetection of each wheel speed sensor is a high speed (shown in FIG.11E), a ratio of the amount of control distributed to the braking unitcontroller 33 is made to be higher than that of the case of a low speed(shown in FIG. 11E). The characteristics are set as described above.

The characteristic of strength and weakness of an amount of control isshown in FIG. 10. In FIG. 10, “rear dif” is a rear differential gearcontroller 31 (a drive force moving mechanism 15 for moving a driveforce between the right and the left wheel), “center dif” is a centraldifferential gear controller 32 (a differential limiting mechanism 19for limiting a differential between the front and the rear wheel, and“brake” is a braking unit controller 33 (braking unit 21L, 21R, 22L,22R). In FIG. 10, “high”, “middle” and “low” respectively show anabsolute value of each device, that is, “high”, “middle” and “low”respectively show a relation between the hydraulic values of thedevices. Values of these “high”, “middle” and “low” are previouslystored in ECU 40A.

Since the turning behavior control device of a vehicle of the secondembodiment of the present invention is composed as described above, thefollowing action and effect can be provided. The contents will beexplained referring to the flow chart shown in FIGS. 12 to 14.

As shown in FIG. 12, in step S41, the control yaw moment calculatingportion 41 reads in a steering angle detected by the steering anglesensor, a vehicle speed detected by each vehicle speed sensor 45 and anactual yaw rate detected by the yaw rate sensor 48. At the same time,US/OS judging portion 42 reads in a lateral acceleration detected by Gsensor 49.

In step S42, the control yaw moment calculating portion 41 calculates atarget yaw rate according to the steering angle and the vehicle speedwhich have been read in. The control yaw moment calculating portion 41calculates a control yaw moment by comparing this target yaw rate withthe actual yaw rate.

After that, in step S43, a map (FIGS. 11A to 11E) corresponding to thespeed, acceleration and deceleration is selected. In steps S44 and S46,according to the control yaw moment and the lateral acceleration, US/OSjudging portion 42 judges whether over-steering (OS) is generated in thevehicle 1, under-steering (US) is generated in the vehicle 1 or neitherunder-steering (US) nor over-steering (OS) is substantially generated inthe vehicle 1.

In the case where US/OS judging portion 42 judges that the vehicle 1A isin a state in which over-steering is generated, the program proceeds tostep S45 and OS suppression control, which is a sub-routine, is carriedout. On the other hand, in the case where US/OS judging portion 42judges in step S46 that the vehicle 1A is in a state in whichunder-steering is generated, the program proceeds to step S47 and USsuppression control, which is a sub-routine, is carried out. In the casewhere US/OS judging portion judges that neither under-steering norover-steering is substantially generated in the vehicle, the program isreturned as it is.

Next, OS suppression control and US suppression control will beexplained below. OS suppression control shown in FIG. 13 judges whetheror not the control yaw moment can be satisfied by carrying out thetorque moving control (the rear differential gear control) between theright rear wheel 14R and the left rear wheel 14L by the reardifferential controller 31 in step S51.

In the case where it is judged that the control yaw moment can besatisfied by carrying out the rear differential gear control, the reardifferential gear control is carried out in step S52, so that adifference in torque between the right rear wheel 14R and the right leftwheel 14L can he adjusted. In this way, over-steering generated in thevehicle 1A is suppressed.

On the other hand, in the case where it is judged that the control yawmoment can not be satisfied even when the rear differential gear controlis carried out, in step S53, the rear differential gear control and thecontrol (the central differential gear control) of controlling a degreeof the limitation of a differential motion between the front wheel 8 andthe rear wheel 14 executed by the center differential controller 32 arecarried out. Due to the foregoing, it is judged whether or not thecontrol yaw moment can be satisfied.

Tn the case where it is judged that the control yaw moment can besatisfied by carrying out the rear differential gear control and thecentral differential gear control, in step S54, the rear differentialgear control and the central differential gear control are carried out.Due to the foregoing, a difference in torque between the right rearwheel 14R and the left rear wheel 14L and a limitation of a differentialmotion between the front wheel and the rear wheel 14 are adjusted sothat over-steering generated in the vehicle 1A can be suppressed.

On the other hand, in the case where it is judged that the controlmoment can not be satisfied even when the rear differential gear controland the central differential gear control are carried out, in step S55,in addition to the rear differential gear control and the centraldifferential gear control, the control (the braking control) executed bythe braking unit controller 33, in which a braking force given to theouter turning wheel is made to be stronger than a braking force given tothe inner turning wheel, is carried out, so that over-steering generatedin the vehicle 1A can be suppressed.

US suppression control shown in FIG. 14 will be explained below. In stepS61, it is judged whether or not the control yaw moment can be satisfiedby carrying out the rear differential control. In the case where it isjudged that the control yaw moment can be satisfied by carrying out therear differential gear control, in step S62, the rear differential gearcontrol is carried out, so that a difference in torque between the rightrear wheel 14R and the left rear wheel 14L can be adjusted andunder-steering generated in the vehicle 1A can be suppressed.

On the other hand, in the case where it is judged that the controlmoment can not be satisfied only when the rear differential gear controlis carried out, in step S63, in addition to the rear differentialcontrol, the braking control is carried out, so that under-steeringgenerated in the vehicle 1 can be suppressed.

As described above, in the present embodiment, an amount of thedistribution of control made by the central differential controller 32at the time of deceleration of the vehicle is set to be smaller thanthat at the time of acceleration of the vehicle. Due to the foregoing, alimitation of the differential motion at the time of suppression of theyawing motion in the process of deceleration is small and braking of therear wheels 14R, 14L can be reduced. Therefore, over-steering can beeffectively suppressed. Especially at the time of deceleration, theturning performance of the vehicle can be stabilized.

In the case where the yawing motion of the vehicle 1A can not besufficiently suppressed even by the rear differential gear controller 31and the center differential controller 32, a braking force given to theouter turning wheel is increased by the braking unit controller 33.Therefore, while a deterioration of the acceleration performance isbeing suppressed, the turning performance of the vehicle 1A can beenhanced and the drive feeling can be enhanced.

In the present embodiment, in the same manner as that of the firstembodiment, in the case of suppressing a yawing motion of the vehicle1A, a drive force given to the inner turning wheel is increased and abraking force given to the outer turning force is increased. In the caseof facilitating a yawing motion of the vehicle 1A, a drive force givento the outer turning wheel is increased and a braking force given to theinner turning force is increased. Therefore, the turning performance ofthe vehicle can be enhanced. Further, amounts of the distribution ofcontrol distributed to the rear differential controller 31 and thebraking unit controller 33 are variably controlled. Therefore, ascompared with the constitution in which amounts of the distribution ofcontrol are fixed, the constitution of the present embodiment canflexibly cope with a state of the vehicle and the drive feeling can beenhanced.

That is, in the case of facilitating a yawing motion of the vehicle (atthe time of the generation of US), a ratio of the amount of controldistributed to the rear differential controller 31 is made to be higherthan a ratio of the amount of control in the case of suppressing ayawing motion of the vehicle 1 (at the time of the generation of OS) Inthis way, a drive force of the outer turning wheel, the ground contactload of which is heavy, is increased, so that the yawing motion controlcan be effectively executed. In the case of suppressing a yawing motionof the vehicle (at the time of the generation of OS), a ratio of theamount of control distributed to the braking unit controller 33 is madeto be higher than a ratio of the amount of control in the case offacilitating a yawing motion of the vehicle 1 (at the time of thegeneration of US). In this way, a braking force given to the outerturning wheel, the ground contact load of which is heavy, is increasedand the yawing motion control is effectively executed and the turningperformance can be stabilized.

In the case where the vehicle 1A is accelerated and the map shown inFIG. 11B is selected in step S43 shown in FIG. 12, a ratio of the amountof control distributed to the rear differential controller 31 is made tobe higher than a ratio of the amount of control in the case ofdeceleration shown in FIG. 11C. Therefore, at the time of accelerationat which a ground contact load of the wheel is increased, a drive forcecan be enhanced and the yawing motion control can be effectivelyexecuted. Accordingly, while a feeling of deceleration at the time ofacceleration is being reduced, the turning performance can be stabilizedand the drive feeling can be enhanced. In the case where the vehicle 1Ais decelerated and the map shown in FIG. 11C is selected in step S43shown in FIG. 12, a ratio of the amount of control distributed to thebraking unit controller 33 is made to be higher than a ratio of theamount of control in the case of acceleration shown in FIG. 11B.Therefore, even when a load given to the wheel is decreased at the timeof deceleration, a reduction of the lateral force given to the wheel,which is caused by a difference in the drive force between the right andthe left wheel, can be suppressed. Accordingly, the turning performanceat the time of deceleration can be stabilized.

In the present embodiment, in the case where the vehicle 1A is runningat a low speed and the map shown in FIG. 11E is selected in step S43shown in FIG. 12, a ratio of the amount of control distributed to therear differential controller 31 is made to be higher than a ratio of theamount of control in the case where the vehicle is running at a highspeed shown in FIG. 11D. In the case where the vehicle 1A is running ata high speed and the map shown in FIG. 11D is selected in step S43 shownin FIG. 12, a ratio of the amount of control distributed to the brakingunit controller 33 is made to be higher than a ratio of the amount ofcontrol in the case where the vehicle is running at a low speed shown inFIG. 11E. Accordingly, while a feeling of deceleration, which is causedby an excessive increase in the braking force, is being suppressed,under-steering and over-steering can be properly suppressed and theturning performance of the vehicle can be enhanced.

The embodiment of the present invention has been explained above.However, it should he noted that the present invention is not limited tothe above specific embodiment. Variations can be made without departingfrom the spirit and the scope of the present invention.

In the above embodiment, the front differential gear 6 is a torqueinduction type differential gear which mechanically restricts adifferential motion made between the right 8R and the left wheel 8Laccording to an intensity of torque inputted from the engine 2. However,it should be noted that the present invention is not limited to theabove specific embodiment. For example, the drive force moving mechanism15 for moving a drive force between the right and the left wheel may hearranged not only in the rear differential gear 12 but also in the frontdifferential gear 6. Alternatively, the drive force moving mechanism 15for moving a drive force between the right and the left wheel may bearranged only in the front differential gear 6.

In the above embodiment, explanations are made into the case in whichthe vehicle 1 is a four-wheel drive vehicle. However, the vehicle 1 isnot especially limited to a four-wheel-drive vehicle. The vehicle 1 maybe a front-wheel drive vehicle. Alternatively, the vehicle 1 may be arear-wheel drive vehicle.

In the above embodiment, explanations are made into the case in whichwhen the rear differential controller 31 controls the drive force movingmechanism 15 for moving a drive force between the right and the leftwheel, a difference between the torque transmitted from the engine 1 tothe right rear wheel 14R and the torque transmitted from the engine 1 tothe left rear wheel 14L is adjusted. However, it should be noted thatthe present invention is not limited to the above specific embodiment.For example, drive forces of electric motors, which are respectivelyarranged on the front wheel side or the rear wheel side, may beindependently adjusted. In this connection, in this case, other than anelectric motor, another drive source such as an engine may be mounted onthe vehicle.

Instead of the drive force moving mechanism 15 for moving a drive forcebetween the right and the left wheel, a mechanism of distributing adrive force between the right and the left wheel may be used. Forexample, the following constitution may be adopted. When clutchmechanisms are respectively arranged in the right and the left wheel andfastening forces of these clutch mechanisms are adjusted, intensities ofthe drive forces transmitted to the right and the left wheel may bechanged. Further, this constitution may be applied to the rear wheelside or the front wheel side.

In the above embodiment, a judgment of under-steering/over-steering ismade according to the control yaw moment obtained by the control yawmoment calculating portion 41 and according to the acceleration in thelateral direction of the vehicle 1 measured by G sensor 49. However, itshould be noted that the present invention is not limited to the abovespecific embodiment. As long as it is possible to judge a turning stateof the vehicle, any structure may be adopted.

In the above embodiment, the speed information is detected by thevehicle speed sensors 45L, 45R, 46L, 46R. However, it should be notedthat the present invention is not limited to the above specificembodiment. For example, the following constitution may be adopted.Low-speed-corner/high-speed-corner is estimated from the detectioninformation sent from the steering wheel angle sensor 47 and a map isselected according to the thus estimated value.

In the above embodiment, an acceleration of the vehicle in thelongitudinal direction is detected by G sensor 49. However, the presentinvention is not limited to the above specific embodiment. For example,when a vehicle speed is differentiated, a longitudinal acceleration isestimated and a map may be selected from this estimated value.Alternatively, when a longitudinal acceleration is estimated from anoutput torque of the engine 2, a total reduction ratio of thetransmission 3 and a braking torque of the braking unit 21L, 21R, 22L,22R, a map may be selected according to thus estimated value.

In the above embodiment, the differential limiting mechanism 19 forlimiting a differential between a front and a rear wheel is of the geartype. However, the present invention is not limited to the abovespecific embodiment. As long as it has the same function, any typedifferential limiting mechanism may be used.

1. A device operable to control a turning of a vehicle, comprising: afirst adjuster, operable to adjust a drive force applied to at least oneof front wheels and rear wheels of the vehicle; a second adjuster,operable to adjust a braking force applied to at least one of the frontwheels and the rear wheels; a first detector, operable to detect anacceleration and deceleration of the vehicle and a motion controller,operable to provide a control amount which is distributed to the firstadjuster with a first ratio and to the second adjuster with a secondratio, the motion controller operable to: control the first adjuster soas to increase the drive force applied to the at least one of the frontwheels and the rear wheels situated in an inner side of the turning, andcontrol the second adjuster so as to increase the braking force appliedto at least one of the front wheels and the rear wheels situated in anouter side of the turning, in order to suppress yawing of the vehicle;control the first adjuster so as to increase the drive force applied toat least one of the front wheels and the rear wheels situated in anouter side of the turning, and control the second adjuster so as toincrease the braking force applied to at least one of the front wheelsand the rear wheels situated in an inner side of the turning, in orderto facilitate the yawing; increase the first ratio in a case that thefirst detector detects the acceleration; and increase the second ratioin a case that the first detector detects the deceleration.
 2. Thedevice according to claim 1, further comprising a second detector,operable to detect a velocity of the vehicle, wherein: the motioncontroller is operable to increase the first ratio in a case that thevelocity detected by the second detector is less than a prescribedvalue; and the motion controller is operable to increase the secondratio in a case that the velocity detected by the second detector is noless than the prescribed value.
 3. The device according to claim 1,wherein: the motion controller is operable to increase the first ratioin order to facilitate the yawing; and the motion controller is operableto increase the second ratio in order to suppress the yawing.
 4. Thedevice according to claim 1, further comprising a third adjuster,operable to adjust a degree of limiting a differential motion betweenthe front wheels and the rear wheels, wherein: the motion controller isoperable to control at least two of the first adjuster, the secondadjuster and the third adjuster; and the motion controller is operableto decrease a control amount which is distributed to the third adjusterin a case that the first detector detects the deceleration.
 5. Thedevice according to claim 4, further comprising a third detector,operable to detect a value correlated to a target yawing momentum of thevehicle, wherein the motion controller is operable to control the secondadjuster so as to increase the braking force applied to at least one ofthe front wheels and the rear wheels situated in an outer side of theturning, in order to suppress yawing of the vehicle, in a case that thevalue correlated to the target yawing momentum is not satisfied even ifthe first adjuster and the third adjuster are controlled.